There are many applications today where it is desired to sense the presence and location of a specific object, as for example, a package stored in a warehouse or on a pallet or in a shipping container. For example, a warehouse attendant or shipping clerk may need to determine whether a particular package or item is present and where it is located. When there are many packages or items that are similar in appearance this can be a daunting and very time consuming task. Ordinarily, the attendant would have to examine the label on every package or item looking for the desired item or package. The advent of bar-code identification has somewhat simplified such tasks, but suffers from the limitation that each bar code label must be located and physically scanned at close range by a bar code reader. Every item or package in the pile may have to be scanned before the user can even be sure whether or not the desired package or item is or is not present. This can be extremely time consuming and inefficient.
Radio frequency identification (RFID) tags are now in common use with many goods or items. An RFID tag is an electronic device attached to an item or package and contains a unique identifier (e.g., an ID number) that can be read remotely using a radio frequency (RF) signal. When the RFID tag is interrogated by an RFID tag reader, the tag responds with at least its unique identifier. Many different types of RFID tags are now in use. For example, and not intended to be limiting: (i) some tags are substantially passive, that is, they don't emit a signal but their presence in the antenna field of the interrogator dynamically alters the impedance of the interrogator's RF antenna allowing their presence to be detected; (ii) some are semi-passive, that is, they receive a signal from the interrogator on a first frequency and use the received energy to reply on a second frequency; and (iii) some are active, that is, they have an on-board power source for the tag circuit, which is turned on by the interrogation signal so that the tag can broadcast a response. Any of these and other types of tags can be used with the present invention provided that the RFID interrogator can determine the unique tag identifiers. The tag identifier is therefore associated with the item to which the tag is attached. When the tags are within radio frequency (RF) signaling distance of the interrogator they respond. If the unique identifier (e.g., the ID number) of the desired item is among those scanned by the interrogator, then the user will know that it is present within the signaling range of the RFID interrogator, but may still not know its exact location. If the warehouse or other storage location is equipped with tag range measuring infrastructure, then the infrastructure system may also be able to determine the location of the tagged object or package. However, not all package or item storage locations have such infrastructure. So, a need continues to exist for a means and method that will determine the presence and location of a particular item or package without such RFID ranging infrastructure.
Accordingly, it is desirable to provide an improved means and method for remotely determining the presence and position of tagged items or packages. It is desirable that such system and method be capable of working with the many types of RFID tags that already exist. In addition, it is desirable that such system and method be simple, rugged and reliable. It is further desirable that such system and method not require fixed infrastructure but be portable and self-contained so that it can be used anywhere. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.